1. Field of the Invention
The present invention relates to a developing apparatus used in an image forming apparatus of electrophotographic or electrostatic recording type as a copying machine, a printer and the like and adapted to develop an electrostatic latent image on an image bearing member.
2. Related Background Art
In image forming apparatuses of electrophotographic or electrostatic recording type, an electrostatic latent image on an image bearing member has been developed by a developing apparatus containing a developing agent.
In the past, as shown in FIG. 14A, in order to prevent magnetic toner from leaking through a gap between a developing frame 12 containing the magnetic toner and a developing roller 9c for supplying the magnetic toner contained in the developing frame 12 to an electrophotographic photosensitive drum, as a sealing means for sealing gaps between the developing frame 12 and the developing roller 9c at both longitudinal ends of the developing roller 9c, elastic members 51 made of felt, rubber or the like have been used.
At a lower part of the developing roller 9c, sealing has been effected by abutting a sheet member 52 provided on the developing frame 12 against the lower part of the developing roller 9c along a longitudinal direction of the developing roller. Further, both longitudinal ends of the sheet member 52 have been pinched between the elastic members 51 and the developing roller 9c to prevent the magnetic toner from leaking through both longitudinal ends.
Alternatively, as shown in FIG. 14B, at both longitudinal ends of the developing roller 9c, sealing (for magnetic toner) has been effected by magnetic forces of magnets 63 disposed around peripheral surfaces of the both longitudinal ends of the developing roller 9c with small gaps "g" therebetween.
However, in the above-mentioned examples, as shown in FIG. 14A, when the elastic members 51 made of felt, rubber or the like are used as the sealing means between both longitudinal ends of the developing roller 9c and developing frame 12, since the both longitudinal ends of the sheet member 52 are pinched between the elastic members 51 and the developing roller 9c, both longitudinal ends of sheet member 52 abut against both longitudinal ends of the developing roller 9c without any gap. Thus, there is an advantage that the magnetic toner can surely be prevented from leaking through both longitudinal ends, but, in such an arrangement, an assembling operation is troublesome, and, since both longitudinal ends of the developing roller 9c are elastically urged by the elastic members 51, when the developing roller 9c is rotated, great load is generated to increase the rotational torque of the developing roller 9c.
On the other hand, as shown in FIG. 14B, when the magnets 63 are used as the sealing means between the both longitudinal ends of the developing roller 9c and the developing frame 12, since the magnets 63 do not abut against the developing roller 9c, the assembling operation becomes easy and the rotational torque of the developing roller 9c can be reduced. However, since there are small gaps g between the developing roller 9c and the magnets 63, the magnetic toner remains at opposed portions between the both longitudinal ends of the developing roller 9c and the magnets 63, with the result that the magnetic toner may be accumulated on the ends of the sheet member 52 abutting against the lower part of the developing roller 9c. In such a case, as shown in FIG. 14B, the accumulated magnetic toner forcibly urges the sheet member 52 downwardly to form gaps "h" between the developing roller 9c and the sheet member 52, with the result that the magnetic toner may leak through the gaps h.